59-416: Poposauroidea is a clade of advanced pseudosuchians . It includes poposaurids , shuvosaurids , ctenosauriscids , and other unusual pseudosuchians such as Qianosuchus and Lotosaurus . It excludes most large predatory quadrupedal " rauisuchians " such as rauisuchids and " prestosuchids ". Those reptiles are now allied with crocodylomorphs (crocodile ancestors) in a clade known as Loricata , which
118-525: A clade (from Ancient Greek κλάδος (kládos) 'branch'), also known as a monophyletic group or natural group , is a grouping of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree . In the taxonomical literature, sometimes the Latin form cladus (plural cladi ) is used rather than the English form. Clades are
177-479: A "ladder", with supposedly more "advanced" organisms at the top. Taxonomists have increasingly worked to make the taxonomic system reflect evolution. When it comes to naming , this principle is not always compatible with the traditional rank-based nomenclature (in which only taxa associated with a rank can be named) because not enough ranks exist to name a long series of nested clades. For these and other reasons, phylogenetic nomenclature has been developed; it
236-465: A ' sail ' like that of certain " pelycosaurs " (like Dimetrodon ) and spinosaurids . Lotosaurus and shuvosaurids were toothless and presumably beaked herbivores while Qianosuchus , Poposaurus and ctenosauriscids were sharp-toothed predators. The ecological disparity of many members of this clade means that it is difficult to assess what the ancestral poposauroid would have looked like. Poposauroids can be differentiated from other pseudosuchians by
295-623: A clade can be described based on two different reference points, crown age and stem age. The crown age of a clade refers to the age of the most recent common ancestor of all of the species in the clade. The stem age of a clade refers to the time that the ancestral lineage of the clade diverged from its sister clade. A clade's stem age is either the same as or older than its crown age. Ages of clades cannot be directly observed. They are inferred, either from stratigraphy of fossils , or from molecular clock estimates. Viruses , and particularly RNA viruses form clades. These are useful in tracking
354-521: A clade containing only the Sauropodomorpha and Herrerasauridae . Thomas Holtz (2017) recommended using the name Sauropodomorpha to refer to a possible clade that includes traditional sauropodomorphs and herrerasaurids; alternatively, he proposed redefining the long-disused taxon Pachypodosauria to include Sauropodomorpha and Herrerasauridae as subclades. Cau (2018) also supported Ornithoscelida but placed herrerasaurids, Tawa and Daemonosaurus in
413-404: A few ornithosuchids and aetosaurs as well as a variety of dinosaurs (most commonly in ornithischians and theropods) In almost all archosariforms, the sacral ribs of the first primordial sacral vertebra contact the ilium near the base of that bone, close to its contact with the pubis. Poposauroids had first primordial sacral ribs with additional forward branches, which lie on the inner edge of
472-435: A form unlike the vertebrae of these archosauriforms, and Nesbitt concluded that it was an "insertion", formed from the innermost sections of the two primordial vertebrae. Although this process is not unique to poposauroids, it is only known in a few other archosaur lineages, such as Batrachotomus , silesaurids , and dinosaurs . Basal poposauroids such as Arizonasaurus and Qianosuchus only had three sacral vertebra, with
531-457: A lack of limb material in ctenosauriscids means that it is unknown whether this trait was basal to the group as a whole. Missing data for ctenosauriscids also obscures when certain traits of the caudal vertebrae and ankle bones were gained or lost within Poposauroidea. Franz Nopcsa first used the term Poposauridae in 1923 to refer to poposauroids. At this time, the sole member of the group
590-907: A large cladistic analysis, Sterling J. Nesbitt (2011) found Xilousuchus to be a poposauroid most closely related to Arizonasaurus . Nesbitt's analysis did not recover a monophyletic Rauisuchia or monophyletic Rauisuchoidea. Poposauroidea was found to be monophyletic, and more resolved than in previous analyses, with Qianosuchus as the most basal member of the group and Lotosaurus grouping with shuvosaurids instead of ctenosauriscids. The cladogram below follows Nesbitt (2011) with clade names based on previous studies. Qianosuchus [REDACTED] Arizonasaurus [REDACTED] Xilousuchus Poposaurus [REDACTED] Lotosaurus [REDACTED] Sillosuchus Effigia [REDACTED] Shuvosaurus [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] Clade In biological phylogenetics ,
649-493: A monophyletic Saurischia, according to its traditional definition. Instead, the group was found to be paraphyletic . As a solution, Theropoda was removed from the group and placed as the sister group to the Ornithischia in the newly defined clade Ornithoscelida . As another result, the authors redefined Saurischia as "the most inclusive clade that contains D[iplodocus] carnegii , but not T[riceratops] horridus ", resulting in
SECTION 10
#1732876130560708-481: A new group called Paracrocodyliformes . Brusatte et al. (2010) conducted a phylogenetic study of archosaurs that resulted in a grouping referred to as Poposauroidea. Unlike many recent studies, they found Rauisuchia to be monophyletic , consisting of two major clades: Rauisuchoidea and Poposauroidea. The monophyly of Rauisuchia was not strongly supported in Brusatte et al.' s analysis. They noted that if their tree
767-422: A revised taxonomy based on a concept strongly resembling clades, although the term clade itself would not be coined until 1957 by his grandson, Julian Huxley . German biologist Emil Hans Willi Hennig (1913–1976) is considered to be the founder of cladistics . He proposed a classification system that represented repeated branchings of the family tree, as opposed to the previous systems, which put organisms on
826-490: A row extending down the neck and body. In all poposauroids, the tip of the fibula (outer shin bone) is symmetrical and straight when seen from the side, rather than slanted as in other non-crocodylomorph pseudosuchians. Those more advanced than ctenosauriscids had flattened hooflike pedal unguals (toe claws). Some poposauroids had very short arms compared to the length of their legs, although disarticulation in Qianosuchus and
885-511: A similar hip anatomy independently of each other, possibly as an adaptation to their herbivorous or omnivorous diets. In his paper naming the two groups, Seeley reviewed previous classification schemes put forth by other paleontologists to divide up the traditional order Dinosauria. He preferred one that had been put forward by Othniel Charles Marsh in 1878, which divided dinosaurs into four orders: Sauropoda , Theropoda , Ornithopoda , and Stegosauria (these names are still used today in much
944-429: A suffix added should be e.g. "dracohortian". A clade is by definition monophyletic , meaning that it contains one ancestor which can be an organism, a population, or a species and all its descendants. The ancestor can be known or unknown; any and all members of a clade can be extant or extinct. The science that tries to reconstruct phylogenetic trees and thus discover clades is called phylogenetics or cladistics ,
1003-499: Is also used with a similar meaning in other fields besides biology, such as historical linguistics ; see Cladistics § In disciplines other than biology . The term "clade" was coined in 1957 by the biologist Julian Huxley to refer to the result of cladogenesis , the evolutionary splitting of a parent species into two distinct species, a concept Huxley borrowed from Bernhard Rensch . Many commonly named groups – rodents and insects , for example – are clades because, in each case,
1062-471: Is in turn included in the mammal, vertebrate and animal clades. The idea of a clade did not exist in pre- Darwinian Linnaean taxonomy , which was based by necessity only on internal or external morphological similarities between organisms. Many of the better known animal groups in Linnaeus's original Systema Naturae (mostly vertebrate groups) do represent clades. The phenomenon of convergent evolution
1121-501: Is known in Poposaurus or Lotosaurus ). In addition, most poposauroids possessed elongated necks, and all of them had long and thin cervical ribs . This second neck trait contrasts with the condition in other pseudosuchians, phytosaurs , and pterosaurs, which have short and stout cervical ribs. The neural spines of the dorsal (back) vertebrae are thin and plate-like, even in members of Poposauroidea without sails. This differs compared to
1180-515: Is responsible for many cases of misleading similarities in the morphology of groups that evolved from different lineages. With the increasing realization in the first half of the 19th century that species had changed and split through the ages, classification increasingly came to be seen as branches on the evolutionary tree of life . The publication of Darwin's theory of evolution in 1859 gave this view increasing weight. In 1876 Thomas Henry Huxley , an early advocate of evolutionary theory, proposed
1239-489: Is still controversial. As an example, see the full current classification of Anas platyrhynchos (the mallard duck) with 40 clades from Eukaryota down by following this Wikispecies link and clicking on "Expand". The name of a clade is conventionally a plural, where the singular refers to each member individually. A unique exception is the reptile clade Dracohors , which was made by haplology from Latin "draco" and "cohors", i.e. "the dragon cohort "; its form with
SECTION 20
#17328761305601298-713: Is the sister taxon to the poposauroids in the clade Paracrocodylomorpha . Although it was first formally defined in 2007, the name "Poposauroidea" has been used for many years. The group has been referred to as Poposauridae by some authors, although this name is often used more narrowly to refer to the family that includes Poposaurus and its close relatives. It was phylogenetically defined in 2011 by Sterling Nesbitt as Poposaurus gracilis and all taxa more closely related to it than to Postosuchus kirkpatricki , Crocodylus niloticus (the Nile crocodile), Ornithosuchus woodwardi , or Aetosaurus ferratus . Poposauroids went extinct at
1357-581: The Greek sauros ( σαῦρος ) meaning 'lizard' and ischion ( ἴσχιον ) meaning 'hip joint') is one of the two basic divisions of dinosaurs (the other being Ornithischia ), classified by their hip structure. Saurischia and Ornithischia were originally called orders by Harry Seeley in 1888 though today most paleontologists classify Saurischia as an unranked clade rather than an order. All carnivorous dinosaurs (certain types of theropods ) are traditionally classified as saurischians, as are all of
1416-638: The birds and one of the two primary lineages of herbivorous dinosaurs, the sauropodomorphs . At the end of the Cretaceous Period , all saurischians except birds became extinct in the course of the Cretaceous–Paleogene extinction event . Birds, as a group of maniraptoran theropod dinosaurs, are a sub- clade of saurischian dinosaurs in phylogenetic classification . Saurischian dinosaurs are traditionally distinguished from ornithischian dinosaurs by their three-pronged pelvic structure, with
1475-402: The braincase possesses a pit from where the internal carotid arteries may exit the brain . In early poposauroids, these pits migrated to the underside of the braincase, thereby resembling the primitive condition seen in archosaur relatives such as Euparkeria and proterochampsians . Nevertheless, this reversion is undone in shuvosaurids (and possibly earlier, although no braincase material
1534-402: The ischium which is below and behind the acetabulum. The ilium is a large, complex bone, with a forward-pointing (preacetabular) process, a rear-pointing (postacetabular) process, and a lower portion which forms the upper edge of the acetabulum. In most archosaurs, the lower portion of the ilium is wedge-shaped, forming the inner face of a "closed" acetabulum. In poposauroids the lower portion of
1593-421: The neural arches (the portion of the vertebrae above the spinal cord ) were fused in some ctenosauriscids ( Arizonasaurus ) but not others ( Bromsgroveia ), and were also fused in all poposauroids more advanced than the ctenosauriscids. Unlike most pseudosuchians, poposauroids lack bony scutes known as osteoderms . The only exception to this is Qianosuchus , which possessed numerous tiny osteoderms, lying in
1652-470: The pubis pointed forward. The ornithischians' pelvis is arranged with the pubis rotated backward, parallel with the ischium , often also with a forward-pointing process, giving a four-pronged structure. The saurischian hip structure led Seeley to name them " lizard -hipped" dinosaurs, because they retained the ancestral hip anatomy also found in modern lizards and other reptiles. He named ornithischians "bird-hipped" dinosaurs because their hip arrangement
1711-578: The Stegosauria and Ornithopoda in the Ornithischia, and the Theropoda and Sauropoda in the Saurischia. Furthermore, Seeley used this major difference in the hip bones, along with many other noted differences between the two groups, to argue that "dinosaurs" were not a natural grouping at all, but rather two distinct orders that had arisen independently from more primitive archosaurs . This concept that "dinosaur"
1770-589: The clade can be determined, particularly in the structure of the snout and pelvis (hip). Many of these features are examples of convergent evolution with dinosaurs , with bipedal poposauroids such as Poposaurus and shuvosaurids having been mistaken for theropod dinosaurs in the past. Poposauroidea was a diverse group of pseudosuchians, containing genera with many different ecological adaptations. Some ( Poposaurus and shuvosaurids) were short-armed bipeds , while others (ctenosauriscids and Lotosaurus ) were robust quadrupeds with elongated neural spines, creating
1829-515: The course of their evolution . Nesbitt (2011) argued that additional sacral vertebrae formed between these two "primordial" vertebrae. He gave the well-preserved sacrum of the poposauroid Arizonasaurus as evidence to this process. Poposauroids have three to four sacral vertebrae, with the last and third-to-last vertebrae articulating with the ilium in a way similar to the two primordial vertebrae of more primitive archosauriformes such as Euparkeria and phytosaurs. The second-to-last vertebra has
Poposauroidea - Misplaced Pages Continue
1888-555: The end of the Triassic period along with other non-crocodylomorph pseudosuchians. They were among the most diverse and longest lasting members of non-crocodylomorph Pseudosuchia, with Xilousuchus (a ctenosauriscid) living near the very beginning of the Triassic and Effigia (a shuvosaurid) surviving up until near the end of the Triassic. Despite the high level of diversity and anatomical disparity within Poposauroidea, certain features of
1947-472: The exception of other pseudosuchians. "Group X" was formally given the name "Poposauroidea" by Jonathan C. Weinbaum and Axel Hungerbühler in 2007. In their paper, Weinbaum and Hungerbühler described two new skeletons of Poposaurus and incorporated several new characters of the genus into a phylogenetic analysis. Poposauroidea was recovered as a monophyletic grouping, while other rauisuchians (namely Rauisuchidae and Prestosuchidae) were placed as basal forms of
2006-566: The front edge of the maxilla becoming concave as well. Although these snout features are rare among pseudosuchians, they are much more common in certain avemetatarsalians (bird-line archosaurs) such as pterosaurs and saurischian dinosaurs . The rear branch of the maxilla tapers in most poposauroids, with the exception of Qianosuchus . This contrasts with loricatans, in which this branch is rectangular in shape. Poposauroids also possess several features which are unusual compared to archosaurs in general. For example, in most archosaurs each side of
2065-451: The fundamental unit of cladistics , a modern approach to taxonomy adopted by most biological fields. The common ancestor may be an individual, a population , or a species ( extinct or extant ). Clades are nested, one in another, as each branch in turn splits into smaller branches. These splits reflect evolutionary history as populations diverged and evolved independently. Clades are termed monophyletic (Greek: "one clan") groups. Over
2124-546: The group consists of a common ancestor with all its descendant branches. Rodents, for example, are a branch of mammals that split off after the end of the period when the clade Dinosauria stopped being the dominant terrestrial vertebrates 66 million years ago. The original population and all its descendants are a clade. The rodent clade corresponds to the order Rodentia, and insects to the class Insecta. These clades include smaller clades, such as chipmunk or ant , each of which consists of even smaller clades. The clade "rodent"
2183-425: The holotype, and so they assigned those specimens to the new genera Lythrosuchus and Chatterjeea . In 2005, Sterling Nesbitt noted that "ctenosauriscids" such as Arizonasaurus , Bromsgroveia , and Lotosaurus shared many similarities with "poposaurids" such as Poposaurus , Sillosuchus , and " Chatterjeea " (now known as Shuvosaurus ). He proposed that they formed a clade (informally named " Group X ") to
2242-513: The idea that the former had evolved directly from the latter, possibly by way of an enigmatic family that seemed to possess characters of both groups, the segnosaurs . However, it was later found that segnosaurs were an unusual type of herbivorous theropod saurischian closely related to birds , and the Phytodinosauria hypothesis fell out of favor. A 2017 study by Matthew Grant Baron, David B. Norman and Paul M. Barrett did not find support for
2301-413: The ilium did not evolve until the clade containing Poposaurus and the shuvosaurids. For example, the supraacetabular crest projects downward, rather than outward in this clade. This trait is rare in archosaurs, only evolving independently in a few early theropod dinosaurs such as Coelophysis and Dilophosaurus . Another feature is the presence of an additional diagonal crest which branches upward from
2360-420: The ilium is concave, creating a partially to completely "open" acetabulum formed by open space instead of bone. The only other archosaurs with open hip sockets are dinosaurs and (to a lesser extent) crocodylomorphs. The upper edge of the acetabulum is formed by a pronounced ridge on the ilium, known as a supraacetabular rim or crest. Although all poposauroids possessed open acetabula, most other specializations of
2419-423: The ilium's preacetabular blade. In poposauroids more advanced than Qianosuchus , the sacral vertebrae fuse into a single bone, the sacrum. This fusion occurred incrementally, at different portions of the vertebra. For example, the zygapophyses fused together as early as the ctenosauriscids. The centra (main cylindrical portion) of the sacral vertebrae also may have fused as early as the ctenosauriscids. The bases of
Poposauroidea - Misplaced Pages Continue
2478-590: The last few decades, the cladistic approach has revolutionized biological classification and revealed surprising evolutionary relationships among organisms. Increasingly, taxonomists try to avoid naming taxa that are not clades; that is, taxa that are not monophyletic . Some of the relationships between organisms that the molecular biology arm of cladistics has revealed include that fungi are closer relatives to animals than they are to plants, archaea are now considered different from bacteria , and multicellular organisms may have evolved from archaea. The term "clade"
2537-518: The latter term coined by Ernst Mayr (1965), derived from "clade". The results of phylogenetic/cladistic analyses are tree-shaped diagrams called cladograms ; they, and all their branches, are phylogenetic hypotheses. Three methods of defining clades are featured in phylogenetic nomenclature : node-, stem-, and apomorphy-based (see Phylogenetic nomenclature§Phylogenetic definitions of clade names for detailed definitions). The relationship between clades can be described in several ways: The age of
2596-402: The main premaxillary body. The posterodorsal process, which wraps below the nares to contact the maxilla on the side of the snout, possesses the opposite state. It is much shorter in poposauroids (compared to other pseudosuchians), restricted to only a portion of the lower edge of the nares. This has the added effect of allowing the maxilla to form the rest of the hole's lower and rear edge, with
2655-444: The pubis has a consistent width. Theropod dinosaurs and a few other archosaurs have a distal part of the pubis which is thinner than the proximal part. Shuvosaurids and Lotosaurus also possessed ischia (on either side of the body) which were fused to each other at the midline of the body. Although the ancestral archosaur only had two sacral (hip) vertebrae , many different archosaur groups acquired additional sacral vertebrae over
2714-481: The same way to refer to suborders or clades within Saurischia and Ornithischia). Seeley, however, wanted to formulate a classification that would take into account a single primary difference between major dinosaurian groups based on a characteristic that also differentiated them from other reptiles. He found this in the configuration of the hip bones, and found that all four of Marsh's orders could be divided neatly into two major groups based on this feature. He placed
2773-463: The second vertebra being the 'insertion'. More advanced poposauroids such as Poposaurus and shuvosaurids have four sacral vertebrae, the third recognizable as the insertion. This means that the first vertebra must have been another addition, seemingly the last dorsal vertebra which had been repurposed and transformed into a sacral vertebra. This incorporated dorsal vertebra called a dorsosacral. They were irregularly distributed among archosaurs, known in
2832-792: The spread of viral infections . HIV , for example, has clades called subtypes, which vary in geographical prevalence. HIV subtype (clade) B, for example is predominant in Europe, the Americas and Japan, whereas subtype A is more common in east Africa. Saurischia 1st row (early saurischians): Herrerasaurus ischigualastensis ( herrerasaur ), Eodromaeus murphi ( basal theropod ); 2nd row ( theropods ): Pelecanus occidentalis , Tyrannosaurus rex ; 3rd row ( sauropodomorphs ): Apatosaurus louisae , Plateosaurus trossingensis . Saurischia ( / s ɔː ˈ r ɪ s k i ə / saw- RIS -kee-ə , meaning "reptile-hipped" from
2891-431: The structure of the tip of the snout, particularly the premaxillary bone which lies in front of the nares ( nostril holes). This bone possesses two bony extensions ("processes") which wrap around the nares. The anterodorsal process, which wraps above the nares to contact the nasal bones on the top edge of the snout, is typically quite short in pseudosuchians. Poposauroids have elongated anterodorsal processes, longer than
2950-405: The supraacetabular rim. Although such a crest evolved independently in a number of different archosaurs, this specific subset of poposauroids is unique in having the crest be inclined forward (rather than vertical) and confluent with the elongated preacetabular blade, which is another derived feature of the clade. The pubis and ischium were also specialized in poposauroids. In every other archosaur,
3009-429: The two bones contact each other on the lower edge of the acetabulum. In poposauroids other than Qianosuchus and Lotosaurus , the bones did not touch, leaving the acetabulum open from the sides and below. The width of the pubis is variable at different parts of its shaft. The portion near the acetabulum is thickened, but the tip of the bone (except in Qianosuchus ) is very thin when seen head-on. In most other archosaurs,
SECTION 50
#17328761305603068-501: The two dinosaurian groups has stood the test of time, and has been supported by modern cladistic analysis of relationships among dinosaurs. A node-base clade, Eusaurischia , was named for the least inclusive group containing sauropodomorphs (represented by Cetiosaurus ) and theropods (represented by Neornithes ). Any saurischian that diverged before the theropod-sauropodomorph split is therefore outside clade Eusaurischia. One alternative hypothesis challenging Seeley's classification
3127-403: The vertebrae of most other early pseudosuchians (as well as Euparkeria and phytosaurs), which have neural spines that expand outward to form a flat, rectangular surface when seen from above. Like other reptiles, the pelvis of poposauroids is formed by three plate-like bones: the ilium which lies above the acetabulum (hip socket), the pubis which is below and in front of the acetabulum, and
3186-448: Was Poposaurus , which was considered to be a theropod dinosaur . Over the following years, poposauroids were placed in various groups, including Saurischia , Theropoda , and Carnosauria . This classification existed up until the 1970s, when better remains indicated that Poposaurus was a pseudosuchian rather than a dinosaur. Other genera such as Sillosuchus and Shuvosaurus were later erected. Like Poposaurus , Shuvosaurus
3245-487: Was enlarged by one step, Poposauroidea fell outside Rauisuchia to become the sister group of Ornithosuchidae, which is thought to closely related to, but outside, Rauisuchia. In their tree, Poposauroidea included genera usually classified as poposauroids as well as several other genera that were not previously placed in the group. One of these genera, Qianosuchus , is unique among pseudosuchians in its semiaquatic lifestyle. In his massive revision of archosaurs which included
3304-434: Was an outdated term for two distinct orders lasted many decades in the scientific and popular literature, and it was not until the 1960s that scientists began to again consider the possibility that saurischians and ornithischians were more closely related to each other than they were to other archosaurs. Although his concept of a polyphyletic Dinosauria is no longer accepted by most paleontologists, Seeley's basic division of
3363-528: Was originally thought to be a theropod dinosaur. Sankar Chatterjee reclassified poposauroids as theropod dinosaurs with his description of the new genus Postosuchus in 1985. Chatterjee even considered poposauroids to be the ancestors of tyrannosaurs . Postosuchus was widely considered to be a poposauroid for the next ten years and was included in many phylogenetic analyses of Triassic archosaurs. In 1995, Robert Long and Phillip A Murry noted that several specimens referred to Postosuchus were distinct from
3422-494: Was proposed by Robert T. Bakker in his 1986 book The Dinosaur Heresies . Bakker's classification separated the theropods into their own group and placed the two groups of herbivorous dinosaurs (the sauropodomorphs and ornithischians) together in a separate group he named the Phytodinosauria ("plant dinosaurs"). The Phytodinosauria hypothesis was based partly on the supposed link between ornithischians and prosauropods , and
3481-518: Was superficially similar to that of birds, though he did not propose any specific relationship between ornithischians and birds. However, in the view which has long been held, this "bird-hipped" arrangement evolved several times independently in dinosaurs, first in the ornithischians, then in the lineage of saurischians including birds ( Avialae ), and lastly in the therizinosaurians . This would then be an example of convergent evolution : avialans, therizinosaurians, and ornithischian dinosaurs all developed
#559440